The present invention relates generally to apparatus used in connection with coal mining and more particularly to a bunker having a given storage capacity adaptable for utilization to have bulk materials such as coal fed thereinto and discharged therefrom. The bunker of the present invention is particularly suitable for use in subsurface mine hauling and is of the type which operates to have its volume varied by contraction and expansion of the bunker or container.
Horizontally arranged extensible bunkers which operate to receive and discharge bulk materials and which include means to compensate for temporary fluctuations in the delivery and withdrawal rates of the device are known in the prior art. The commercial utility and economic desirability of extensible bunkers relies to a great extent upon the storage capacity of such bunkers as well as the overall cost per cubic meter of the bunker. Such costs tend to be especially high in installations where the bunker volume is less than about 100 m.sup.3.
However, in the case of extensible bunkers of limited storage capacity there develops a rapidly increasing demand especially where the seam and run-of-mine coal are on the same level and where, as a result, a blind shaft spiral cannot be fitted ahead as a buffer. Additionally, the same situation arises in drift work for the stowing of the heap or pile of materials which has been extracted which may then be hauled away at a later time and in proportioned amounts. Furthermore, smaller bunkers tend to have a greater inclination to develop bridging or arching and to reducing the size of the coal in larger bunkers.
Mechanical discharge devices which are utilized in the bottoms of smaller bunkers are more susceptible than those utilized with larger installations to the shifting of the supporting structure which may occur as a result of expansion or swelling of the mine floor.
Removal or trickle or leakage passing between the bottom and the transport means may cause disproportionately higher costs for smaller extensible bunkers than for larger bunkers.
Many of the disadvantages which arise with prior art devices involving extensible bunkers of limited storage capacity may be avoided mainly by improving the discharge capabilities of the bulk material. With known extensible bunkers, the discharge is effected by chain scraper conveyors or plate conveyors.
In German No. DT-AS1235841 a device for unloading a transport container is described which, after certain changes have been effected could find use additionally as an extensible bunker. The evacuation of such a container is effected by pushers in stepped arrangement one above the other which are actuated by hydraulic cylinders.
The use of such a device in connection with extensible bunkers is, of course, prohibited when coal is involved because it would result in intensive relative movement within the bulk material and cause undesirable crumbling of the coal. The cost of machinery for a design according to the aforementioned German DT-AS is higher than for the known extensible bunkers in relation to the available storage capacity and attainable output.
Additionally, the evacuation of a container as is illustrated in, for example, German No. DT-AS1054377, by means of a trough conveyor in the bottom thereof having a plurality of pivotal bottom flaps is unsuitable in an extensible bunker because of the disintegration of the coal which will occur in the trough conveyor. Furthermore, problems arise because of the insufficient cross-section of the bottom flaps for material which may involve large lumps and because of the high percentage of trickle or leakage which is to be expected.
It is an object of the present invention to provide an extensible bunker where there is involved the transport of small quantities of material and more specifically where a bunker volume of preferably less than 100 m.sup.3 is involved. The invention is directed toward enabling redesigning and developing of known extensible bunkers thereby avoiding the aforementioned disadvantages and to a large extent to obtaining additional advantages over the presently known art.